The present invention relates to a vibration generating device for generating a vibration by alternately guiding a high pressure fluid to both sides of a vibration-generating piston.
Generally, an engineering/construction machine such as a hydraulic shovel (excavator) is used for digging up earth and sand, ground levelling, piling, etc. Such work is carried out in a manner of operating a boom cylinder, arm cylinder and bucket cylinder of the hydraulic shovel, as necessity requires, to scoop earth and sand by a bucket, or pushing the pile against the earth. Where the bucket hits a great stone while the earth and sand are dug up as described above, if a high frequency vibration is given to the bucket to increase digging force, the great stone can be easily dug up. This is an experientially known fact. Further, it is also known that if the vibration at a short period is given to the bucket when performing the ground levelling, piling or shaking off the earth and sand applied on the bucket, these operations can be carried out smoothly in a short time.
Therefore, as disclosed in JP-A-9-105140, in order to improve workability, it has been proposed to replace a bucket link coupling the tip (tilt link) of a piston rod of a bucket cylinder with the bucket by a vibration actuator for generating the vibration at the site of working as necessity requires so that the vibration generated by the vibration actuator is transmitted to the bucket. The vibrator actuator includes a block-shaped casing with a pair of supply openings for supplying high pressure fluid and an exhaust opening for exhausting low pressure fluid; a vibration-generating piston which is housed slidably in a cylinder formed within the casing; a rotary valve which is connected to the one supply opening and exhaust opening through a supply passage and an exhaust passage, respectively and also connected to both cylinder chambers on both sides of the vibration-generating piston through a pair of fluid passages, and rotates to communicate the supply passage with the cylinder chambers on both sides alternately to guide the high pressure fluid to both cylinder chambers, alternately; and a fluid motor which is housed in the casing and connected to the other supply passage and exhaust passage through a high pressure passage and a low pressure passage, respectively, and is operated by the high pressure fluid supplied through the high pressure passage to provide rotary force to the rotary valve. A flow rate control valve for controlling the flow rate of a high pressure fluid supplied to the fluid motor is attached to the stem of an arm. The flow rate control valve and a main operating valve are connected by a single high pressure conduit, the flow rate control valve and the pair of supply opening of the vibration actuator are connected by a pair of (two) high pressure conduits, and the exhaust opening of the vibration actuator and the main operating valve are connected by a single low pressure conduit.
However, in the conventional vibration generating device described above, when the bucket link is replaced by the vibration actuator, the vibration actuator must be connected to the flow rate control valve and the main operating valve using three conduits. This work is troublesome. In addition, the main operating valve, flow rate control valve and vibration actuator must be connected to one another using four conduits, as described above. This make the structure complicate. Further, use of many conduits may produce leakage of liquid at the conduit coupling portion and damage of the conduits due to their rubbing against each other. This attenuates the reliability of the vibration generating device.